Second try. I like the clean defined lines much better. Learning!

Nice job :) The structure looks great, but maybe you could push for more line width variation? There are many things you can consider for which lines should be thick or thin, such as light, rhythm, overlap, closeness to the viewer and overall contrast. One immediate thing you could try though - for a technical drawing like this - is to keep contour lines and overlap lines thicker, while keeping lines that describe surface iniside an object thin. Ultimately (in my opinion) you want the lines to move, change and be lively, but the rule of "thick line for overlap and contour, and thin line for surface lines" is an easy rule to start applying that is used extensively in technical illustration.